Spiritual Kin Selection

By Steve Roels

If life has evolved to self-replicate, why should one organism help another at a cost to itself when the other is not offspring? Simple tit-for-tat exchanges explain much social behavior in nature but, in many cases, benefits seemingly flow in only one direction without reciprocity. Even casual natural historians know of self-sacrificing behaviors like ground squirrels acting as community predator sentinels, warning non-offspring of danger at considerable risk to themselves.

This evolutionary conundrum vexed Darwin, but he eventually recognized that promotion of kin can extend beyond immediate offspring. Following the discovery of DNA, another British evolutionary biologist, W.D. Hamilton, postulated that behavior appearing “altruistic” was largely governed by the degree of genetic relationship between individuals. Like Darwin, he recognized that individuals could be related to one another in more ways than just direct descent; what matters is the replication of genetic material, not the familial relationship per se. Hamilton formalized his “rule” mathematically as rB>C, where r is the coefficient of genetic relationship (percentage of genetic material identical by descent) between two organisms, B is the benefit to the receiver, and C is the cost to the altruist. For a given behavior, if the degree of relatedness times the benefit is greater than the cost this behavior should be favored by natural selection.

A simple example: Roughly half of my genes are identical by descent with my brother’s genes (r = 0.5) because we share parents. My brother has two daughters and, though they are not my daughters, I am certainly interested in their welfare. From an evolutionary perspective, I should be, since those charming girls have a quarter of my genes (they get half their dad’s genes, which are half of mine, so r = 0.25). In fact, I should be so interested in their welfare that I should be willing to consider sacrificing my own life for the lives of my brother and his daughters. His genes (50%) and his daughters’ genes (25% each) sum to 100%—equivalent to my own set of genetic material. Apologies to my sister-in-law, who is apparently on her own (r = 0)!

While this scenario may seem a cold calculation, Hamilton’s Rule has been tested empirically in many species and is a compelling explanation for a variety of curious animal behaviors, like birds that forgo reproduction in order to help their siblings or cousins find more mates or raise more young. In fact, this type of reasoning has blossomed into a subfield of evolutionary biology known as the study of kin selection. So what of altruism? Is it all just selfish genes and indirect evolutionary benefits?

Since kin selection effectively explains away many apparently altruistic behaviors in nature, some evolutionary biologists have argued that true altruism (i.e. no direct or indirect benefits to the giver) does not exist. After all, truly altruistic behaviors impose costs on an individual without any genetic benefit and should be disfavored by natural selection.

However, there are intriguing examples of animals demonstrating self-sacrificing behavior to assist genetically unrelated individuals. In one carefully controlled lab study, researchers found rats would forgo food rewards in order to release a genetically unrelated individual trapped in a flooded compartment [1]. In the wild, there are stories of “animal altruists” whose behavior is difficult to explain in terms of benefits to the altruist, even in the most diffuse, indirect, or long-term manner. This is especially true in incidents of inter-species altruism; dolphins have defended humans from sharks and humpback whales were once observed rescuing a doomed seal from a pod of killer whales. What benefit could the dolphins or humpbacks possibly have received?

Humans are, of course, animals too and only the boldest scientists claim humans are not capable of true altruism. However, if truly altruistic behavior exists in more species than just humans, it suggests that such behaviors have some biological underpinning, even if one regards humans as having some unique moral abilities or obligations that do not have their origins in our DNA.

Biologists may eventually work out a coherent theory for the evolution of altruism. Regardless of whether they do or not, it seems humanity’s troubles exceed what an evolved altruism can effectively remedy. Thankfully, we have another model for altruism; one that transcends the limits that evolutionary math or genetic constraints might impose on love and empathy. According to Hamilton’s Rule, I could rationally sacrifice myself for two brothers (r = 0.5*2 = 1.0), but Jesus taught his disciples that the greatest love is to lay down one’s life for a friend (r = 0).

Jesus makes for a compelling example of what we could call “spiritual kin selection.” My genetic relationship to the biological Jesus is r = 0. Yet Jesus proclaimed that we both have the same Father in heaven and even willingly sacrificed his own life for me and others “dead in sin.” By reuniting the human family in this way, Jesus gives us, in a sense, a new “r” with each other, a kind of spiritual relatedness. Indeed, Jesus regularly uses the language of kinship with his disciples, calling them his brothers and sisters, a tradition that continues to this day among Christian believers. Perhaps our spiritual kinship is an explanation, or at least justification, of true altruism toward our fellow human?

We can take our spiritually-enabled altruism even further than this, for Jesus did not stop his redemption at species boundaries. Paul makes it clear in both Romans (8:18-22) and Colossians (1:15-20) that Jesus’ redemption extends to the whole of creation, including non-human species. If so, the depth of human relationships with other species needs to be reconsidered in a post-Easter universe. This insight can be traced back at least as far as the 13th century; in hagiographies of the saint, Francis of Assisi regularly refers to animals and even natural forces as “Brother” and “Sister” and preaches the Good News to the birds. The saint’s 21st century standard-bearer, Pope Francis, has rekindled this awareness, writing that the created things are “linked by unseen bonds and together form a kind of universal family" [2]. It is only this spiritual kinship that can empower the kind of altruism necessary in a broken world desperate for beings who put others ahead of themselves.​1. Sato et al. 2015. Animal Cognition 18(5): 1039-1047.2. Francis. 2015. Laudato Si’: On Care for Our Common Home [Encyclical].

Bio: Steve Roels holds a bachelor's in biology from Calvin College and a master's in ecology and evolutionary biology from the University of Kansas. He is currently finishing up a PhD in Integrative Biology at Michigan State University. He is a member of River Terrace Christian Reformed Church in East Lansing, MI.